Robotics Tech Papers
Five Steps Towards Using Less Energy Per Pick
by Josef Karbassi, Vice President Automation Division
PIAB USA, Inc. Posted 05/01/2014
Cutting-edge energy saving technology can make a real difference to industry. Apart from reducing energy bills and tax levies, it helps companies become more sustainable and environmentally sound. Using less energy makes more than simply economic sense. The vacuum technology used for materials handling is one area in the production process where substantial energy savings can be made. This step by step guide is intended to help you use less energy per picked item.
Step 1: Don’t be tempted to use electromechanical pumps Proponents of electromechanical technology will raise their eyebrows at this advice, as it is true that an electromechanical pump operating next to an ejector pump will use less energy. The two-step approach of an ejector pump, in which the electric power is first transferred into compressed air, inevitably leads to losses and makes the technology about 40-50 percent less efficient than its electromechanical counterpart. However, in reality, such simplistic comparisons are not applicable. Instead, you need to look at how the different technologies are implemented.
First, the pumps have very different space requirements. Ranging in size from a little finger to a brick, an ejector pump can be placed close to where the vacuum is needed. This reduces the effect of energy losses and improves efficiency. Overall, it allows a more decentralized and more energy efficient plant layout, see Step 5. In contrast, an electromechanical pump, in size equivalent to anything from a vacuum cleaner to a trailer, requires a more central position. Secondly, it is easy to set up an ejector pump to switch on and off during each duty cycle, so that it is operating only during 50 percent of the cycle. Such intermittent operation is not possible in an electromechanical pump as it is impossible to stop its rotating fans during each cycle. An electromechanical pump will have to operate continuously, resulting in more or less constant energy demand. The ability to switch the pump on and off is particularly useful for the handling of non-leaking materials such as sheets of glass or metal. For certain applications, it is possible to reduce the energy consumption by 90-99 percent.
Step 2: Employ a multistage ejector The ejector’s efficiency is obviously an important parameter to focus on for minimized energy consumption. The ejector efficiency is determined by the vacuum performance relative to the air consumption. Two main types of ejectors are used in sealed vacuum handling systems – single-stage ejectors and multistage ejectors. The multistage design is more complex, but is also 15-50 percent more efficient. State-of-the-art multistage vacuum ejectors can reach the required vacuum levels up to twice as fast as single-stage ejectors, with the same energy consumption. The faster air evacuation time of the multistage ejector results in a much improved suction capacity. The trade-off is a slight increase in size. However, multistage vacuum ejectors in the form of nozzle cartridges with built-in flap valves and filters are small enough to be integrated directly into suction cup fittings. Such cartridges are offered in several sizes, making them suitable for all applications. Another advantage of multistage ejectors is that they display a particularly favorable flow chart for vacuum in the region of 30-50 percent. This is the vacuum level normally needed for picking up leaky materials such as corrugated cardboard boxes.
Step 3: Optimize the vacuum level and the release function Just as thermostats help modern radiators to maintain a constant room temperature, there are tools that help vacuum systems to automatically adjust to vacuum levels that are optimal for picking up a particular item. Such tools ensure that the vacuum pump is only running when it is needed and can switch off the pump at the required vacuum level. The installation of energy saving pressure monitors also ensure that pumps are running at an optimal level. Depending on the application, a vacuum level of 70 percent may be unnecessary and can perhaps be reduced to 40 percent, resulting in significantly lower energy consumption.
Other types of optimizers allow the use of atmospheric air rather than compressed air for the release of handled objects. Such passive release systems consume virtually no energy in contrast to active systems in which objects are released through compressed air blowing through the suction cup. Hence, in applications that require an active release mechanism it is particularly important to optimize the amount of time that compressed air is applied.
Step 4: Choose the right suction cups Although they are small, suction cups can greatly impact the energy consumption of a vacuum system. Opting for cups that offer the highest levels of performance can save significant amounts of energy. An enhanced sealing capability, even on non-smooth surfaces, means that less flow capacity is needed from the system to achieve a firm grip on handled objects. Suction cups that are built to collapse and then to return to their original state more easily allow for smaller pumps to be used to complete the task, contributing to further energy savings. Specially engineered and purpose-built suction cups provide greater lifting power compared to conventional alternatives, which means that fewer cups are needed and less energy is used. Suction cups designed to combine a strong and stable body with a high-sealing and soft flexible lip are particularly useful for handling objects with uneven surfaces.
Step 5: Decentralize your vacuum system Finally, there are energy savings to be made in the set-up and overall design of the vacuum system. Systems with one centrally placed vacuum pump are hampered by considerable pipe losses, and the transportation of vacuum requires a lot of energy. Decentralized solutions with multiple pumps are more energy-efficient. In a fully decentralized vacuum system, based on ejector cartridges that integrate the pump in the suction cup, the transportation of vacuum is kept at a minimum. The compressed air is converted into vacuum flow as close as possible to the point in the system where it is needed. As a result, the energy consumption can be greatly reduced, often halved, if a centralized system is replaced by a decentralized system.